1. Field of the Invention
This invention relates to novel synthetic polymers furnishing a controlled release of biologically active component during degradation and to methods of preparing such.
2. Prior Art Relating to the Disclosure
Pesticides having a very long life, such as DDT and other chlorinated hydrocarbons, have been increasingly under attack due to their residues entering the food chain. Pesticides having relatively short lives have been developed; however, the effective life of these pesticides is shortened by washing away, rain, removal by evaporation, degradation into inactive products, or leaching into the subsoil. If the latter occurs, breakdown of the pesticide into nontoxic residues is not as rapid as at the soil-air interface, thus allowing the pesticides to contaminate underground water sources or streams and lakes with subsequent damage to aquatic and wild life.
Work has been done to increase the effective protection period of such pesticides and to diminish the residual waste of costly chemicals which are the causes of serious pollution problems and damage to wild life by designing systems to release the biologically active component at a controlled rate effective to control the pest but minimize the amount leached out by rain, removed by evaporation, or otherwise.
U.S. Pat. Nos. 2,460,376; 3,127,235; and 3,194,730 teach the concept of adsorbing pesticides on strong absorbents such as silica gel, mica and activated charcoal. These formulations have met with only partial success due to the presence of a highly reversible release mechanism.
The use of polymers to control the release of biologically active compounds is known. U.S. Pat. No. 3,074,845 discloses a physical release mechanism in which in inert absorbent is impregnated with a pesticide and then coated with a urea-formaldehyde resin. U.S. Pat. No. 3,223,513 discloses a mixture of an insecticide with a polymer to obtain an extended life product. U.S. Pat. No. 3,212,967 employs a butyl polyacrylate latex with added 0,0-dimethyl-0-(2,4,5-trichlorophenyl)-phosphorothioate. Chlorinated phenols have been incorporated into alkyd resins as esters of tri- or tetra-carboxylic esters of benzene as disclosed in U.S. Pat. No. 3,179,608. U.S. Pat. No. 3,343,941 discloses chemically bonding an herbicide to an alkyd resin by incorporating the herbicide into a reaction mixture of phthalic anhydride or humic acid and glycerol. British Pat. No. 1,212,842 discloses bonding a pesticide directly or through a divalent radical to a polymeric substrate such as forest waste, the chemical bonds between the pesticide and the polymer substrate or divalent radical being hydrolyzable to release the pesticide on a continuous basis.